Arianism

Fourth century heresy, according to the Roman Catholic Church, named for its creator, Arius. Arianism denies the co-equal divinity and co-eternal existence of Jesus Christ, relegating him to a sort of second in command, existing before Creation but after God. (Here's his logic: God is unbegotten, Jesus is begotten, therefore Jesus cannot be equal to his father.)

The Arians relied in their theology on several early versions of the Greekmass and other texts in which Jesus was described as "homoios" to the Father, meaning - resembling or being like the Father. The Council of Nicaea relied on the same texts, but in them the word "homoios" was replaced with the shorter "homos", meaning - identical, one and the same. Many of the theological debates between the two sects revolved around the question of the authenticity of these texts, trying to ascertain who had the earlier version.